Fiddletown hit it on the head. I have not had our lawyer check our leases in a few years, but as the landlord I have the right to restrict certain behavior or items from my property. I can not remember the legal terms our lawyer used to explain all this.
As a renter, I expect you to comply with these terms or leave the premises.
There does not have to be a given reason for me to restrict or require certain things. Maybe I do not like purple cars, but once you sign the lease stating you will not park a purple car in my parking area, you are legally bound not to park it there.
I would talk to the land lord and ask her/him why this clause is there and if there is anyway around it. If it was me, and you promised to park the purple car and cover it, I would probably agree.
(I really do hate purple cars.)